The novel ordered mesoporous NiCo2O4 (meso-NiCo2O4) nanospheres were synthesized by the nanocasting strategy followed by a calcination process for 2-naphthol (2-NAP) and 1-naphthol (1-NAP) individual sensing application. The as-obtained meso-NiCo2O4 material possesses mesoporous structure in spinel crystalline type with a larger specific surface area than other structures. The meso-NiCo2O4-modified carbon paste electrode exhibited excellent electrocatalytic performance for NAP detection by amperometry measurement. The fabricated sensor of 2-NAP and 1-NAP has a wide linear detection range (0.02–300 and 0.02–20 μM) with high sensitivity (1.822 and 1.510 μA μM–1 cm–2) and low limit of detection (0.007 and 0.007 μM), respectively. In addition, the NAP sensors possess excellent reproducibility, stability, and selectivity.Keywords: amperometry; electrochemical sensor; mesoporous nanospheres; naphthol isomers; NiCo2O4;

•A new multilayer ultrathin film (UTF) containing EBT anions and exfoliated nanosheets of Ni–Al LDH was synthesized.•The UTF was synthesized by LBL self-assembly technique and its properties were studied by electrochemical method.•The UTF modified electrode presented a significant electrocatalytic performance towards the oxidation of salicylic acid.A highly sensitive electrochemical sensor, EBT/LDH ultrathin film, for salicylic acid (SA) was fabricated in a facile way based on multilayer ultrathin films (UTFs) containing Eriochrome black T anions (EBT) and exfoliated Ni–Al layered double hydroxide (LDH) nanosheets via layer-by-layer self-assembly technique. The XRD pattern confirms that the products are nickel aluminum hydrotalcites, and SEM images shows continuous and uniform film surface. Electrochemical impedance spectroscopy (EIS), Current – time (i-T) and cyclic voltammetry (CV) methods were used to characterize the electrochemical behavior of the ultrathin film. The electrode modified with ultrathin film displays significantly high electrocatalytic performance for SA with sensitivity of 860 μAmM− 1 cm− 2, large concentrations ranging from 0.01 to 100 μM and with low detection limit 0.003 μM (S/N = 3). The EBT/LDH ultrathin film is shown to be a feasible electrochemical sensor for detection of SA.

•Co3O4-CNF were prepared by electrospinning technology followed by successive annealing process and oxidation process.•Morphology and catalytic property of different weight percentage of cobalt acetate in precursor were studied.•The proposed sensor has good stability and reproducibility.A glassy carbon electrode (GCE) modified with electropun tricobalt tetroxide nanoparticles decorated carbon nanofibers (Co3O4-CNF) were first applied for the determination of l-tryptophan (l-Trp). The synthesized Co3O4-CNF was characterized by scanning electron microscopy, Raman, X-ray diffraction and electrochemical impedance spectroscopy. The electrochemical detection of l-try was successfully conducted in 0.1 M phosphate solution (pH 2). The linear relationship of l-Trp was in the range of 0.005–40 μM and the detection limit reached 0.002 μM (S/N = 3) with little interference from other amino acids.

Uniform, ordered mesoporous ZnCo2O4 (meso-ZnCo2O4) nanospheres were successfully synthesized using a sacrificing template method. The meso-ZnCo2O4 nanospheres were used for the first time for H2O2 biosensing and in glucose biofuel cells (GBFCs) as an enzyme mimic. The meso-ZnCo2O4 nanospheres not only exhibited excellent catalytic performance in the H2O2 sensor, achieving a high sensitivity (658.92 μA·mM–1·cm–2) and low detection limit (0.3 nM at signal-to-noise ratio (S/N) = 3), but also performed as an excellent cathode material in GBFCs, resulting in an open circuit voltage of 0.83 V, maximum power density of 0.32 mW·cm–2, and limiting current density of 1.32 mA·cm–2. The preeminent catalytic abilities to H2O2 and glucose may be associated with the large specific surface area of the mesoporous structure in addition to the intrinsic catalytic activity of ZnCo2O4. These significant findings provide a successful basis for developing methods for the supersensitive detection of H2O2 and enriching catalytic materials for biofuel cells.

The rectangular flake-like mesoporous NiCo2O4 (meso-NiCo2O4) catalysts were first used in glucose bio-sensing and glucose biofuel cell (GBFC) as an enzyme mimic simultaneously. The meso-NiCo2O4 displayed excellent catalytic capability to glucose including a super-fast response time (within 1 s), a super-high sensitivity (662.31 μA (mmol L−1)−1 cm−2), and a super-low detection limit (0.3 nmol L−1 at S/N = 3) on the sensor. On the other hand, meso-NiCo2O4 provided great values in GBFC as anode material with an open circuit voltage of 0.63 V, a maximum power density of 0.092 mW cm−2, and a limiting current density of 1.3 mA cm−2, respectively. The preeminent catalytic abilities may be attributed to the large specific surface area resulting from the mesoporous structure and the surpassing intrinsic catalytic activity of NiCo2O4 itself. These significant findings may promote the development of the supersensitive detection of glucose and will undoubtedly widen the catalytic materials for biofuel cell electrodes.矩形片状介孔NiCo2O4催化剂被首次同时用于非酶葡萄糖传感器和非酶葡萄糖燃料电池中. 结果表明: 在传感器上, 介孔NiCo2O4催化剂对葡萄糖具有优异的传感特性, 如超快的响应时间(小于1 s), 超高的灵敏度(662.31 μA (mmol L−1)−1cm−2)以及超低的检测限(0.3 nmol L−1 at S/N = 3); 在燃料电池上, 介孔NiCo2O4催化剂作为负极材料展示出了良好的应用前景, 包括0.63 V的开路电压, 0.092 mW cm−2的最大输出功率和1.3 mA cm−2的极限电流密度. 该材料对葡萄糖优异的催化能力归因于介孔结构引起的巨大比表面积能够提供更多的活性位点和NiCo2O4本身具有的良好的催化能力. 本研究为促进非酶葡萄糖超敏感检测和丰富非酶葡萄糖燃料电池负极催化材料的发展提供了有利的依据.

In the present study, a new fluorescence probe based on dithizone-etched CdTe nanoparticles was designed for the sensitive and selective detection of cadmium ions in environmental samples via a reversible off–on fluorescence mode. At first, the initial bright fluorescence of L-cysteine-capped CdTe NPs could be effectively quenched in the presence of dithizone (DZ) due to the chemical etching effect, which results from the breaking of Cd–thiol layers by DZ, thus leading to a decrease in the NPs surface passivation. Then, upon the addition of Cd2+, the weak fluorescence of the CdTe NPs–DZ system gradually recovered, owing to the occurrence of Cd–thiol passivation layers on the surface of the NPs. Under optimal conditions, a good linear relationship was obtained in the range from 0.4 μM to 15.4 μM for Cd2+, with a detection limit of 0.13 μM. In addition, this CdTe NPs-based nanosensor presents remarkable selectivity for Cd2+ over other metal ions and was successfully applied for the detection of Cd2+ in real water samples with satisfactory results, demonstrating its potential application for the determination of Cd2+ in the environment.

•Flake-like mesoporous NiCo2O4 was synthesized by a simple hydrothermal method.•The NiCo2O4-decorated reduced graphene oxide composites (NiCo2O4/rGO) were synthesized.•The NiCo2O4/rGO composites were first used as the modified materials for the electrochemical determination of rutin.The glassy carbon electrode (GCE) modified with mesoporous NiCo2O4-decorated reduced graphene oxide (NiCo2O4/rGO) was first applied for the electrochemical determination of rutin. The synthesized NiCo2O4 and NiCo2O4/rGO were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) method. The sensor not only showed a satisfactory linear range (0.1–150 μM) and detection limit (0.01 μM) but also exhibited the good anti-interference abilities, low price, high stability, as well as favorable precision and accuracy. The present work is meaningful to expand functionalized graphene composites to sensor fields and promote the development of rutin sensors.

•We prepared mesoporous Co3O4 by sacrificing template method and a following anneal process.•A very simple and reliable electrochemical platform was fabricated for the electrochemical detection of hydroquinone and catechol.•The platform showed relatively low detection limit and wide liner range in the actual detection process.The Co3O4 electro-catalysts with the mesoporous structure were prepared by the sacrificing template method. The chemical composition, structural and morphological characterizations of Co3O4 were examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-desorption (BET). The electrochemical properties of the meso-Co3O4 were investigated by differential pulse voltammetry (DPV) and cyclic voltammetry (CV) for the simultaneous detection of hydroquinone (HQ) and catechol (CC) in the phosphate buffer media (PBS). Based on the meso-Co3O4 modifier electrode, a sensitive electrochemical sensor for phenolic compounds was successfully fabricated. Under optimal conditions, the detection limits of HQ and CC were found to be 0.1 and 0.1 μΜ (S/N = 3), respectively. The outstanding catalytic capability of meso-Co3O4 catalysts may be associated with their large surface area provided by mesoporous structure.

A glassy carbon electrode modified with poly(L-methionine) and graphene composite film (PLME/GR/GCE) was fabricated by electropolymerization for determination of L-tryptophan (L-Trp) in the presence of dopamine (DA). The morphology and structure of the composite film were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was utilized to investigate the electrocatalytical oxidation of L-Trp from the potentially interfering species on the PLME/GR/GCE. Under optimum conditions, the proposed method exhibited a wide linear dynamic range 0.2–150 μM, with a detection limit (S/N = 3), and good reproducibility and high selectivity. Moreover, the proposed modified electrode has been successfully applied to determine L-Trp in milk and human serum samples.

•NiO–CuO/graphene modified electrode was prepared by electro-deposition.•Graphene was modified by using citric acid to produce more functional groups, which benefits the deposition of dispersed metal particles.•The proposed sensor shows wide linear concentration range and high sensitivity for coinstantaneous determination of dopamine, acetaminophen and tryptophan.In the present work, transition metal oxides decorated graphene (GR) have been fabricated for simultaneous determination of dopamine (DA), acetaminophen (AC) and tryptophan (Trp) using square wave voltammetry. Electro-deposition is a facile preparation strategy for the synthesis of nickel oxide (NiO) and copper oxide (CuO) nanoparticles. GR can be modified by using citric acid to produce more functional groups, which is conducive to the deposition of dispersed metal particles. The morphologies and interface properties of the obtained NiO–CuO/GR nanocomposite were examined by scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. Moreover, the electrochemical performances of the composite film were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode exhibited that the linear response ranges for detecting DA, AC and Trp were 0.5–20 μM, 4–400 μM and 0.3–40 μM, respectively, and the detection limits were 0.17 μM, 1.33 μM and 0.1 μM (S/N=3). Under optimal conditions, the sensor displayed high sensitivity, excellent stability and satisfactory results in real samples analysis.An electrochemical sensor based on transition metal oxides nanoparticles–graphene composite film (NiO–CuO/GR) modified glassy carbon electrode for simultaneously detecting dopamine (DA), acetaminophen (AC) and tryptophan (Trp) was fabricated by using square wave voltammetry.

A glassy carbon electrode modified with cuprous oxide nanoparticles-graphene composite film (Cu2O/GR) was prepared and applied to detect acetaminophen (AC). Scanning electron microscopy, energy dispersive X-ray spectroscopy and electrochemical impedance spectroscopy were applied for characterization of the proposed electrode. Cyclic voltammetry and square wave voltammetry were used to investigate the electrocatalysis oxidation of AC on Cu2O/GR. The linearity ranged from 2.0 × 10− 8 to 1.3 × 10− 6 M with a detection limit of 6.67 × 10− 9 M (S/N = 3) and the calculated sensitivity of 14,397.7 μA mM− 1 cm− 2. Under optimal conditions, the sensor displays good stability and satisfactory results in real samples analysis.An electrochemical sensor based on cuprous oxide nanoparticles-graphene composite film (Cu2O/GR) modified glassy carbon electrode for detecting acetaminophen (AC) was fabricated by electro-deposition.

•A poly(bromocresol green) modified glassy carbon electrode was simply prepared.•The modified electrode was applied for simultaneous determination of UA, DA and AA.•The modified electrode exhibited good electrocatalytic activity to UA, DA and AA.A glassy carbon electrode modified with poly(bromocresol green) was prepared by electropolymerization process for simultaneous determination of uric acid, dopamine and ascorbic acid. The interface morphology and structure of poly(bromocresol green) film were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The simultaneous determination of uric acid (UA), dopamine (DA) and ascorbic acid (AA) in 0.1 M phosphate buffer solution (pH 6.0) was carried out by differential pulse voltammetric technique. Under optimum conditions, the results show that the peaks of three species were well separated. The proposed sensor exhibited linear responses to UA, DA and AA in the ranges of 0.5–200, 0.05–10 and 0.5–1000 μM, respectively. Moreover, the poly(bromocresol green) modified electrode has been successfully applied to determine UA, DA and AA in human serum samples and vitamin C tablets.Electrocatalytic oxidation of UA, DA and AA at poly(bromocresol green) modified glassy carbon electrode were investigated by differential pulse voltammetry. The peak currents of UA, DA and AA increased significantly, and the peak potentials shifted negatively at PBG/GCE, moreover, the peak of DA and AA separate significantly, demonstrating that the proposed methods enhanced the kinetics of the electrochemical process as an efficient promoter.DPVs for 10 μM UA, 0.5 μM DA and 70 μM AA in 0.1 M PBS (pH 6.0) at PBG/GCE (a) and bare GCE (b), and PBG/GCE in blank pH 6.0 PBS (c).

The electrochemical detection of hydrogen peroxide in alkaline solution was performed on a La0.7Sr0.3Mn0.75Co0.25O3 (LSMCO) nanofiber modified carbon paste electrode. Perovskite-type oxide LSMCO nanofibers were prepared by electrospinning and calcination. The morphologies, structures, and electrochemical behaviours of the nanofibers were characterized by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and cyclic voltammetry. The modified electrode shows excellent electrocatalytic activity towards hydrogen peroxide. Under optimal conditions, the linear response was obtained in the range of 0.5–1000 μM, with high sensitivity and a low limit of detection.

A new chiral biosensor fabricated by immobilizing bovine serum albumin (BSA) on gold-nanoparticle-modified glassy carbon electrodes, which could discriminate and detect phenylalanine (Phe) enantiomers, was proposed for the first time. The enantioselectivity was characterized by using scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and square wave voltammetry. The results showed that the BSA-modified electrode could enantioselectively recognize Phe enantiomers, and larger response signals were obtained from L-Phe. The factors influencing the performance of the biosensor were investigated. The enantiomeric composition of the L-/D-Phe mixture could be determined from the calibration curves. The modified electrodes have the advantages of simple operation, rapid detection and low cost.

The electrodeposited graphene (EGR) and cysteic acid (CA) composite (CA/EGR) was fabricated through an electrochemical method for the modification of glassy carbon electrode (GCE). Fourier transform infrared spectroscopy (FT-IR) was carried out to characterize the proposed CA film. The electrochemical performance of the CA/EGR modified GCE (CA/EGR/GCE) was demonstrated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified GCE was designed to act as an electrochemical sensor for isoniazid. The obtained detection linearity at the CA/EGR/GCE ranged from 0.1 to 200 μM with the detection limit of 0.03 μM (S/N = 3). Moreover, the sensor was employed for practical sample analysis with satisfactory recoveries, further validating the reliable practicability for electroanalysis. In addition, CA/EGR/GCE also displayed good reproducibility, high stability and excellent anti-interference ability for the determination of isoniazid.

Based on the quenching of the fluorescence intensity of thioglycolic acid (TGA)-capped core-shell CdTe/ZnS nanoparticles (NPs) by vanillin, a novel, simple and rapid method for the determination of vanillin was proposed. In aqueous medium, the functionalized core-shell CdTe/ZnS NPs were successfully synthesized with TGA as the capping ligand. TGA-capped core-shell CdTe/ZnS NPs were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Factors affecting the vanillin detection were investigated, and the optimum conditions were also determined. Under the optimum conditions, the relative fluorescence intensity of CdTe/ZnS NPs was linearly proportional to vanillin over a concentration range from 9.4 × 10−7 to 5.2 × 10−4 M with a correlation coefficient of 0.998 and a detection limit of 2.6 × 10−7 M. The proposed method was also employed to detect trace vanillin in cookies with satisfactory results.

•PAR/EGR composite film was prepared for the first time.•The sensor can be applied to determinate CPFX in the presence of AA, UA and DA.•The sensor indicated the feasibility in drug samples and biological media.A glassy carbon electrode modified with poly(alizarin red)/electrodeposited graphene (PAR/EGR) composite film was prepared and applied to detect ciprofloxacin (CPFX) in the presence of ascorbic, uric acid and dopamine. The morphology and interface property of PAR/EGR films were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The electrocatalytic oxidation of CPFX on AR/EGR was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The linearity ranged from 4 × 10−8 to 1.2 × 10−4 M with a detection limit (S/N = 3) of 0.01 μM. The modified electrode could be applied to the individual determination of CPFX as well as the simultaneous determination of CPFX, ascorbic acid, uric acid and dopamine. This method proved to be a simple, selective and rapid way to determine CPFX in pharmaceutical preparation and biological media.An electrochemical sensor based on PAR/EGR/GCE via a cooperation of the potentiostatic technique and cyclic voltammetry was first fabricated for the determination of CPFX with satisfied detecting result of real samples.

•The first electrochemical sensor for caffeine (CAF) and vanillin (VAN).•NGR–NCNTs was modified through electrodeposition for the first time.•The sensor was qualified for real sample determination with satisfactory results.A nitrogen-doped graphene/carbon nanotubes (NGR–NCNTs) nanocomposite was employed into the study of the electrochemical sensor via electrodeposition for the first time. The morphology and structure of NGR–NCNTs nanocomposite were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Meanwhile, the electrochemical performance of the glassy carbon electrode (GCE) modified with electrodeposited NGR–NCNTs (ENGR–NCNTs/GCE) towards caffeine (CAF) and vanillin (VAN) determination was demonstrated by cyclic voltammetry (CV) and square wave voltammetry (SWV). Under optimal condition, ENGR–NCNTs/GCE exhibited a wide linearity of 0.06–50 μM for CAF and 0.01–10 μM for VAN with detection limits of 0.02 μM and 3.3 × 10−3 μM, respectively. Furthermore, the application of the proposed sensor in food products was proven to be practical and reliable. The desirable results show that the ENGR–NCNTs nanocomposite has promising potential in electrocatalytic biosensor application.A nanocomposite of nitrogen-doped graphene (NGR) and nitrogen-doped carbon nanotubes (NCNTs) was first modified onto an electrode through electrodeposition method and employed to sensitively detect caffeine and vanillin simultaneously for the first time.

This paper demonstrated an electrochemical sensor based on NiO nanoparticles-graphene composite film (NiO/GR) modified glassy carbon electrode for detecting ascorbic acid (AA) in the presence of folic acid using differential pulse voltammetry. The obtained NiO/GR nanocomposite was fabricated by electro-deposition technology. The morphologies and interface properties of NiO/GR composite film were examined by scanning electron microscopy, energy dispersive X-ray spectroscopy and electrochemical impedance spectroscopy. The modified electrode exhibits excellent sensing performance for detecting AA with linear range from 0.05 to 1100 μM and a detection limit of 0.0167 μM (S/N = 3). Under optimal conditions, the sensor displays excellent stability and satisfactory results in real samples analysis.

•A poly(3,4-ethylenedioxythiophene)/graphene composite film was prepared.•The modified electrode exhibited good electrocatalytic activity to DNA bases.•The sensor showed high sensitivity, wide linear range and high stability.A simple and reliable method for simultaneous determination of purine and pyrimidine (guanine, adenine, thymine and cytosine) was developed at poly(3,4-ethylenedioxythiophene)/electro-deposited graphene modified glassy carbon electrode (PEDOT/GR/GCE). Scanning electron microscopy and electrochemical impedance spectroscopy were used to examine the morphology and interface property of PEDOT/GR film. Differential pulse voltammetry was utilized to investigate the electrochemical behavior of DNA bases in 0.1 M PBS (pH 7.4). The results showed that the peaks of four bases were well separated. The proposed sensor exhibited low detection limit, high sensitivity and wide linear range for simultaneous detection of four DNA bases, with high stability.Electrocatalytic oxidation of purine and pyrimidine at different electrodes was investigated by differential pulse voltammetry. The peak currents of G, A, T, C increased significantly and the peak potentials shifted negatively at PEDOT/GR/GCE, demonstrating that the combination of the excellent properties of GR and PEDOT enhanced the kinetics of the electrochemical process as an efficient promoter.DPVs of GCE (a), GR/GCE (b), PEDOT/GCE (c), PEDOT/GR/GCE (d) in the presence of 20.0 μM G, 20 μM A, 100 μM T and 100 μM C, and PEDOT/GR/GCE (e) in blank pH 7.4 PBS.

We have developed a nonenzymatic electrochemical sensor based on a carbon paste electrode modified with electrospun LaMnO3 fibers for fructose determination. LaMnO3 fibers, a kind of perovskite-type oxide, were prepared by electrospinning and subsequent calcination process. The morphology and structure of LaMnO3 fibers were characterized by scanning electron microscope, X-ray diffraction and Fourier Transform Infrared spectrum. The electrochemical response of the proposed sensor was evaluated by cyclic voltammetry and amperometry. Under optimal conditions, the linear response for fructose determination was obtained in the range of 0.4–100 μM, with a low detection limit of 63 nM (S/N = 3).Graphical abstract(A) SEM image of the as-synthesized LaMnO3 sample; (B) current–time curve of LaMnO3/CPE at different concentrations of fructose (inset: the calibration curve for fructose determination).

A poly-Ni(II)–curcumin (curcumin: 1,7-bis[4-hydroxy-3-methoxyphenyl]-1,6-heptadiene-3,5-dione) composite film modified electrode was prepared for amperometric determination of β-nicotinamide adenine dinucleotide (NADH). Scanning electron microscopy and Energy Dispersive X-ray spectroscopy were used to examine the morphology and interface property of the Ni(II)–curcumin film. Under optimum conditions, the amperometric detection of NADH provided a wide linear detection range (0.3–300 μM), high sensitivity (230.02 μA mM−1 cm−2) and low limit of detection (LOD = 0.18 μM, S/N = 3). Moreover, the modified electrode showed good stability and reproducibility, indicating that it can improve the analysis signal of NADH in a very convenient way.

A novel poly-sulfosalicylic acid-modified glassy carbon electrode (PSA/GCE) was developed for the detection of roxithromycin (RM) and its simultaneous determination with dopamine (DA). The morphologies and interface properties of the PSA film were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Fourier transform infrared (FTIR) spectra indicated that PSA was successfully modified on the electrode. The electro-catalytic oxidation of RM on the PSA/GCE was investigated, individually and simultaneously, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions. The proposed method exhibited a wide linear dynamic range from 2 × 10−8 to 1 × 10−5 M with a low detection limit (S/N = 3) of 6.67 × 10−9 M for roxithromycin. The modified electrode showed good stability, reproducibility and high selectivity, and demonstrated its feasibility for analytical purposes and human serum samples.

In this paper, a novel method was developed for rapid and quantitative determination of cephalexin on the basis of the fluorescence quenching of L-cysteine capped core–shell CdTe/ZnS nanoparticles (NPs). The functionalized CdTe/ZnS NPs were successfully synthesized in aqueous solution. L-Cysteine capped CdTe/ZnS NPs were characterized by the means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Experimental results displayed that the fluorescence intensity of CdTe/ZnS NPs reduced in the presence of cephalexin due to interaction between L-cysteine capped CdTe/ZnS NPs and cephalexin, with the emission wavelength at about 665 nm. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of cephalexin ranging from 3.4 × 10−6 to 1.0 × 10−4 M with a detection limit of 0.83 × 10−6 M. The L-cysteine capped CdTe/ZnS NPs fluorescence probe showed an obvious and good response to cephalexin, and the result was also satisfactory when it was applied to analyzing cephalexin in a real sample.

•A droplet-based microfluidic electrochemical sensor using Pt-black was developed.•The current response on Pt-black increased 10.2 fold compared with on bare Pt.•This sensor has been used for glucose determination in human blood serums.We describe a droplet-based microfluidic electrochemical sensor using platinum-black (Pt-black) microelectrode. Pt-black microelectrode was generated by electrodeposition of Pt nanoparticles on bare Pt microelectrode. Scanning electron microscope (SEM) image displays a flower-like microstructure of Pt nanoparticels. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicate that the Pt-black efficiently decreased the charge transfer resistance and improved the electrocatalytic activity towards oxidation of hydrogen peroxide (H2O2). Compared with bare Pt microelectrode, the current response on Pt-black microelectrode increased 10.2 folds. The effect of applied potential and electrodeposition time has been investigated in detail. The proposed sensor was validated by performing enzyme activity assay in flowing droplets. For demonstration, glucose oxidase (GOx) is chosen as the model enzyme, which catalyzes the oxidation of β-d-glucose to the product H2O2. The enzyme activity of GOx was evaluated by measuring the electrochemical current responding to various glucose concentrations. And the results indicate that this microfluidic sensor holds great potential in fabricating novel glucose sensors with linear response up to 43.5 mM. The analytical applications of the droplet-based microfluidic sensor were tested by using human blood serum samples. Reproducibility, interferences, and long-term stability of the modified electrode were also investigated. The present approach shows the feasibility and great potentials in constructing highly sensitive and low-consumption sensors in the field of droplet microfluidics.

•A preparation tactic of β-cyclodextrin/graphene nanocomposite film was developed.•A sensitive electrochemical sensor for quercetin was successfully manufactured.•The sensor possesses high sensitivity and fast response for detection of quercetin.•The sensor was applied in real samples with satisfactory results.A mild and novel preparation tactics based on electrochemical techniques for the fabrication of electro-deposited graphene (E-GR) and polymerized β-cyclodextrin (P-βCD) nanocomposite film were developed. The structure and morphology of GR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Simultaneously, the electrochemical properties of this nanocomposite were characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Based on the synergistic effect of E-GR and P-βCD, a super-sensitive electrochemical sensor for quercetin was successfully fabricated. Under optimum conditions, the determination range for quercetin was from 0.005 to 20 µM with a low detection limit of 0.001 µM (S/N=3). Moreover, this sensor also displays excellent sensitivity, fine reproducibility and stability. To further study the practical applicability of the proposed sensor, the determination of real samples was carried out with satisfactory results.

•This sensor exhibits excellent electrocatalytic activity toward methotrexate.•Sodium dodecyl benzene sulfonate can keep the oxidation of methotrexate stable.•The sensor was applied in real samples with satisfying results.A simple and sensitive electrochemical sensor based on poly (l-lysine) modified glassy carbon electrode (PLL/GCE) was developed to sensitively detect methotrexate (MTX) in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were carried out to characterize PLL film which exhibits excellent electrocatalytic activity toward the oxidation of MTX in 0.1 M phosphate buffer solution. In addition, the oxidation peak of MTX remained stable at PLL/GCE in the presence of SDBS and its current increased 8 times compared with that at bare GCE without SDBS. Experimental parameters were optimized with regard to pH, electro-polymerization segment, accumulation time and concentration of SDBS. Under optimum conditions, the square wave voltammograms exhibited that the oxidation peak current was linearly proportional to the concentration of MTX in the range of 5 nM – 0.2 μM with detection limit of 1.7 (± 0.06) nM (S/N = 3). Moreover, this method was applied to detect MTX in medicinal tablets with satisfying results.

•A novel system combining concentration gradient generation with electrochemical detection was developed based on droplet microfluidics.•Half maximal inhibitory concentration (IC50) of three types of acetylcholinesterase inhibitors was evaluated.•A whole enzyme inhibition procedure costs only 6 min with concentration gradient spanning 3 orders of magnitude and the reagent consumption reduced 1000-fold.A simple but robust droplet-based microfluidic system was developed for dose–response enzyme inhibition assay by combining concentration gradient generation method with electrochemical detection method. A slotted-vials array and a tapered tip capillary were used for reagents introduction and concentration gradient generation, and a polydimethylsiloxane (PDMS) microfluidic chip integrated with microelectrodes was used for droplet generation and electrochemical detection. Effects of oil flow rate and surfactant on electrochemical sensing were investigated. This system was validated by measuring dose–response curves of three types of acetylcholinesterase (AChE) inhibitors, including carbamate pesticide, organophosphorus pesticide, and therapeutic drugs regulating Alzheimer's disease. Carbaryl, chlorpyrifos, and tacrine were used as model analytes, respectively, and their IC50 (half maximal inhibitory concentration) values were determined. A whole enzyme inhibition assay was completed in 6 min, and the total consumption of reagents was less than 5 μL. This microfluidic system is applicable to many biochemical reactions, such as drug screening and kinetic studies, as long as one of the reactants or products is electrochemically active.

•Spinel-type CoxNi1−xFe2O4 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were synthesized.•CoxNi1−xFe2O4 were first employed as novel enzyme mimic sensing materials of H2O2.•Co0.5Ni0.5Fe2O4/CPE showed excellent electrocatalytic activity to H2O2.•Co0.5Ni0.5Fe2O4/CPE was successfully applied to determine H2O2 in toothpastes.A series of spinel-type CoxNi1−xFe2O4 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) magnetic nanomaterials were solvothermally synthesized as enzyme mimics for the eletroctrocatalytic oxidation of H2O2. X-ray diffraction and scanning electron microscope were employed to characterize the composition, structure and morphology of the material. The electrochemical properties of spinel-type CoxNi1−xFe2O4 with different (Co/Ni) molar ratio toward H2O2 oxidation were investigated, and the results demonstrated that Co0.5Ni0.5Fe2O4 modified carbon paste electrode (Co0.5Ni0.5Fe2O4/CPE) possessed the best electrocatalytic activity for H2O2 oxidation. Under optimum conditions, the calibration curve for H2O2 determination on Co0.5Ni0.5Fe2O4/CPE was linear in a wide range of 1.0 × 10−8–1.0 × 10−3 M with low detection limit of 3.0 × 10−9 M (S/N = 3). The proposed Co0.5Ni0.5Fe2O4/CPE was also applied to the determination of H2O2 in commercial toothpastes with satisfactory results, indicating that CoxNi1−xFe2O4 is a promising hydrogen peroxidase mimics for the detection of H2O2.

Perovskite-type oxide LaNiO3 nanofibers (LNFs) have been successfully synthesized by electrospinning and sequential calcinations. The electrospun LNFs modified carbon paste electrode was used to construct a nonenzymatic hydrogen peroxide (H2O2) sensor and glucose biosensor for the first time. The LNFs composition was verified by X-ray diffraction, and the morphologies were examined by scanning electron microscopy and transmission electron microscopy. Cyclic voltammetry and amperometry were used to evaluate the catalytic activity of the LNFs modified electrode towards H2O2 and glucose. By using LNFs as electrocatalysts, the modified electrode showed high electrocatalytic activity for the oxidation of H2O2 and glucose. Under the optimized conditions, the H2O2 sensor exhibited a low detection limit down to 33.9 nM with a wide linear range from 0.05 to 1000 μM. The nonenzymatic sensor also showed fast response, long-term stability as well as a low detection limit for glucose.

•AuNPs/Parg/CPE was constructed and utilized to determine cefotaxime.•Obviously oxidation performance of cefotaxime to the electrochemical response.•Determination in pharmaceutical formulations and human serum samples.•It showed high stability, repeatability, reproducibility, good sensitivity.A simple and sensitive electrochemical sensor based on Au nanoparticles/poly (L-arginine) modified carbon paste electrode (AuNPs/Parg/CPE) was constructed and utilized to determine cefotaxime. Scanning electron microscope (SEM) image showed that the L-arginine (L-arg) had been electropolymerized on the CPE and the immobilized Au nanoparticles (AuNPs) were spherical in shape. Fourier transform infrared spectra (FTIR) indicated that the poly (L-arginine) (Parg) film was successfully modified on CPE. Electrochemical impedance spectroscopy (EIS) and cyclic voltammogram (CV) illustrated the Parg and AuNPs efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analytes and electrode. The electrooxidation of cefotaxime on the modified electrode was performed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The results showed the response current of cefotaxime at AuNPs/Parg/CPE increased 17 times than that of bare CPE. The calibration curve was linear over the cefotaxime concentration range of 0.01–100.0 μM with a detection limit (S/N = 3) of 2.3 nM. This proposed method has been applied to determine cefotaxime in pharmaceutical formulations and human serum samples, and the results were satisfactory.

•Mn-modified CdTe nanoparticles were synthesized via a facile method at low temperature.•The fluorescence properties and morphology of Mn-CdTe nanoparticles were studied clearly.•Mn-CdTe nanoparticles show superior response to the bovine serum albumin molecular on the fluorescence emission.•This detection method was sensitive and provides a wide range of bovine serum albumin concentrations.Mn-modified CdTe nanoparticles (NPs) were synthesized via a novel, facile method at low temperature. The modified NPs were directly synthesized in aqueous solution by mixing CdCl2·2.5H2O, fresh NaHTe solution, thioglycolic acid (TGA) and MnCl2·4H2O under suitable conditions. Mn-modified CdTe NPs were evaluated as fluorescence probe for bovine serum albumin (BSA) in aqueous solution. Experiment results showed that the fluorescence emission of Mn-modified CdTe NPs was enhanced significantly by BSA, while other substances exhibited no significant effect on NPs. Under the optimal conditions, the response was linearly proportional to the concentration of BSA ranging from 5.0×10−9 to 7.0×10−7 mol/L with detection limit 5.26×10−10 mol/L. Based on the distinct optical properties of Mn-modified CdTe NPs with BSA, Mn-modified CdTe NPs can be developed as a potential identified fluorescence probe for BSA in aqueous solution.

A novel and highly sensitive fluorescence probe has been developed for determination of ascorbic acid (AA) based on the distinct fluorescence quenching of Mn-doped CdTe fluorescence emission in the presence of AA. Mn-doped CdTe quantum dots were prepared by using inorganic salts as precursors and L-cysteine as the stabilizer in an aqueous system. Their optical properties were characterized by ultraviolet-visible spectrometry, spectrofluorometry, structural features by X-ray diffraction spectrometry, transmission electron microscopy, Fourier transform infrared spectrometry, and exact composition by energy dispersive spectrometry, respectively. Under the optimum conditions, the response is linearly proportional to the concentration of AA in the range of 0.4 to 10 nM with an extremely low detection limit of about 0.081 nM. The newly developed method was successfully applied for the determination of AA in pharmaceutical tablets with good recoveries.

We report a sensor platform for the determination of L-tryptophane. It is based on a carbon paste electrode that was modified with LaCoO3 poriferous nanofibers that were synthesized by electrospinning and subsequent thermal treatment. The structures and morphologies of LaCoO3 poriferous nanofibers were characterized by X-ray diffraction spectrum and scanning electron microscopy. The electrochemical performance of the sensor was evaluated by cyclic voltammetry and amperometry, and the results demonstrated that it exhibits strong electrocatalytical activity towards the oxidation of L-tryptophan in 0.1 mol L−1 phosphate buffer solution (pH 3.0). The linear range of L-tyrosine was 5.0 × 10−8 to 5.0 × 10−6 mol L−1 with a low detection limit down to 1.0 × 10−8 mol L−1. Moreover, the modified electrode exhibited high selectivity, long-term stability and fast current response, demonstrating its feasibility for the analytical purpose.

A novel fluorescence probe based on the quenching of fluorescence of bovine serum albumin (BSA) capped ZnS nanoparticles (NPs) has been developed for the determination of gatifloxacin in bulk and pharmaceutical dosage form. The functionalized ZnS NPs were successfully synthesized in aqueous medium, with the biomolecule BSA as the capping ligand. Due to a specific interaction, the fluorescence intensity of ZnS NPs reduces obviously in the presence of gatifloxacin. Under the optimal conditions, the relative fluorescence intensity of ZnS NPs is linearly proportional to gatifloxacin concentration from 2.0 × 10−7 M to 1.0 × 10−4 M with a detection limit of 6.5 × 10−8 M. The proposed method is simple, rapid, practical and can be successfully applied to assay gatifloxacin capsules.Highlights► Nano-ZnS fluorescence probes were synthesized with good optical properties. ► Gatifloxacin were successfully detected by ZnS fluorescence probes. ► Wide linear ranges and low detection limits were obtained.

A novel electrochemical sensor for the determination of p-nitrophenol (PNP) was fabricated with the nanoscaled composite oxide Mg(Ni)FeO-modified carbon paste electrode (CPE), and its electrocatalytic performances were investigated using the cyclic voltammogram and differential pulse voltammetry techniques. The influential factors were optimized such as the mass ratio of Mg(Ni)FeO to graphite, the pH value of buffer solution and the accumulation time at open circuit. The indirect oxidation peak current of PNP was found to be proportional to its concentration between 2.0 × 10−6 and 2.0 × 10−4 M on the proposed sensor Mg(Ni)FeO/CPE under the optimal condition (10 % Mg(Ni)FeO/graphite, pH 5.0 HAc–NaAc, 120 s quiescence). The sensor Mg(Ni)FeO/CPE exhibited a high sensitivity of 811 μA mM−1 cm−2 and a low detection limit of 0.2 μΜ (S/N– = 3) for PNP detection, and got satisfactory results when it was applied to determine PNP in real samples. The results demonstrate that Mg(Ni)FeO/CPE based on the nanomaterial Mg(Ni)FeO with high specific area and mesoporous structure could be employed as an electrochemical sensor for PNP determination with simplicity, low cost, good selectivity, repeatability, and stability.

A novel uracil covalently grafted carbon paste electrode (Ura/CPE) based on electro-deposition of uracil on CPE was prepared for the quantitative determination of nevirapine. The records of electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) in K3Fe(CN)6/K4Fe(CN)6 solution illustrated that uracil grafted on CPE efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analyte and electrode. The electrochemical properties of Ura/CPE towards the oxidation of nevirapine were investigated by cyclic voltammetry and differential pulse voltammetry (DPV) in 0.1 M NaOH. The effects of pH and scan rates on the oxidation of nevirapine were studied. The results indicated the participation of the same protons and electrons in the oxidation of nevirapine, and the electrochemical reaction of nevirapine on Ura/CPE is an adsorption-controlled process. Under optimized conditions, the linearity between the oxidation peak current and nevirapine concentration was obtained in the range of 0.1–70.0 μM with detection limit of 0.05 μM and the sensitivity of 2.073 μA mM−1 cm−2 (S/N = 3). The proposed method was also successfully applied to detect the concentration of nevirapine in human serum samples.

An electrochemical sensor based on tricobalt tetroxide nanoparticles–graphene nanocomposite film modified glassy carbon electrodes (GCEs) for sensitive determination of l-tyrosine (L-Tyr) was presented here. The nanoparticles were fabricated by electro-polymerization technology. Scanning electron microscopy was implemented to characterize morphology of the nanocomposite film. The electron transfer behavior of modified electrodes was investigated in 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical response of modified electrodes toward L-Tyr was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), amperometry in detail. The results indicated that synergistic effect of Co3O4 NPs and graphene film dramatically improved the conductivity and sensitivity of the sensor. Under optimal conditions, a wide linear relationship between the responses and L-Tyr concentrations ranging from 1.0 × 10−8 to 4.0 × 10−5 mol L−1 was obtained with a comparatively low detection limit of 1.0 × 10−9 mol L−1. Furthermore, the sensor also displays excellent sensitivity and high stability. To further study the practical applicability of the fabricated sensor, it was applied to detect real samples and the received results were satisfactory.Graphical abstractAn electrochemical sensor based on Co3O4/GR/GCE was fabricated for sensitive determination of l-tyrosine (L-Tyr) with sensitive detection limit and satisfied detecting result of real samples.Highlights► Electropolymerization was employed to prepare GR/GCE. ► The Co3O4/GR/GCE presents a considerable low detection limit. ► The sensor showed satisfactory result as an amperometric detector for drug samples.

A novel cysteic acid modified carbon paste electrode (cysteic acid/CPE) based on electrochemical oxidation of l-cysteine was developed to simultaneously determine ofloxacin and gatifloxacin in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectra (FTIR) indicated that l-cysteine was oxidated to cysteic acid. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) indicated that cysteic acid was successfully modified on electrode. The large peak separation (116 mV) between ofloxacin and gatifloxacin was obtained on cysteic acid/CPE while only one oxidation peak was found on bare electrode. And the peak currents increased 5 times compared to bare electrode. Moreover, the current could be further enhanced in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate. The differential pulse voltammograms (DPV) exhibited that the oxidation peak currents were linearly proportional to their concentrations in the range of 0.06–10 μM for ofloxacin and 0.02–200 μM for gatifloxacin, and the detection limits of ofloxacin and gatifloxacin were 0.02 μM and 0.01 μM (S/N = 3), respectively. This proposed method was successfully applied to determine ofloxacin and gatifloxacin in pharmaceutical formulations and human serum samples.Highlights► Cysteic acid modified electrode based on electrochemical oxidation of l-cysteine ► Simultaneous detection of ofloxacin and gatifloxacin ► Obviously catalytic performance to the electrochemical response ► Determination in pharmaceutical formulations and human serum samples ► It showed high stability, repeatability, reproducibility, good sensitivity.

In this work, a glassy carbon electrode modified with poly-sulfosalicylic acid (PSA/GCE) was prepared using electropolymerization method and applied for the determination of l-tryptophan (l-Trp) in the presence of ascorbic acid and dopamine. The morphologies and interface properties of PSA film were examined by scanning electron microscopy and electrochemical impedance spectroscopy. The electrocatalytic oxidation of l-Trp on the PSA/GCE from potentially interfering species, e.g. ascorbic acid (AA) and dopamine (DA) was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimum conditions, the proposed method exhibited wide linear dynamic range of 5 × 10−8 to 1 × 10−5 M with a detection limit (S/N = 3) of 6.8 × 10−9 M. Moreover, the modified electrode exhibited good reproducibility and high selectivity, demonstrating its feasibility for the analytical purpose.

A novel poly(l-proline)-ordered mesoporous carbon film with controllable thickness on the glassy carbon electrode surface was fabricated by one-step electrochemical technique and further used for the construction of electrochemical sensing platform of natural estrogens. Scanning electron microscopy, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy were employed to characterize the surface morphology, structure and interface property of the polymer. The voltammetric behaviors of estrogens involving estradiol, estrone and estriol were investigated on the modified electrode, and the proposed electrode exhibited strong electrocatalytic activity toward the oxidation of three estrogens especially for estradiol, making it a promising electrochemical sensing platform for sensitive detection of estrogens. Under the optimum conditions, the linear range of estradiol obtained by square-wave voltammetric determination was 1.0 × 10−8–2.0 × 10−6 mol/L with a low detection limit of 5.0 × 10−9 mol/L. The developed modified electrode was also applied to the determination of estradiol in female blood serums with satisfactory results.

A highly sensitive and selective nonenzymatic glucose sensor based on electrodepositing NiO nanoparticles on ordered mesoporous carbon (named as NiO/OMC) modified glassy carbon electrode (GCE) was constructed. The synthesized OMC was characterized by X-ray diffraction, and the morphology images of OMC nanoparticle and NiO/OMC nanocomposite were characterized by scanning electron microscope. Electrochemical behaviors of glucose at the NiO/OMC/GCE were investigated by cyclic voltammetry and amperometry, and the modified electrode showed excellent electrochemical activity toward the oxidation of glucose. At the optimum conditions, the calibration curve for glucose determination was linear in the range of 2–1000 μM with a fast response time (<2 s), and a high sensitivity of 834.8 μA mM−1 cm−2 and a low detection limit (S/N = 3) of 0.65 μM were obtained. In addition, the proposed sensor was successfully applied to analyze glucose level in human blood serum samples.Graphical abstractA novel NiO/OMC composite was fabricated for the nonenzymatic glucose sensing, and the proposed sensor was successfully applied to analyze glucose level in human blood serum samples.Highlights► A novel nonenzymatic glucose electrochemical sensor was proposed. ► The sensor was based on nickel(II)oxide/ordered mesoporous carbon modified glassy carbon electrode. ► The developed sensor exhibited wide linear range and high sensitivity. ► The as-made sensor was also successfully applied to determine glucose content in clinic serum sample.

A thin film of poly(eriochrome black T) was deposited on the surface of glassy carbon electrode by cyclic voltammetry, and this system is shown to enable the sensitive determination of adenine (A) and guanine (G). Scanning electron microscopy, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy were carried out to characterize the film which exhibits excellent electrocatalytic activity toward the oxidation of A and G in 0.1 M phosphate buffer solution (pH 4.0). Square wave voltammetry reveals an oxidation peak at 1084 mV whose current is linearly related to the concentration of A in the range from 0.05 to 1.00 μM. The oxidation peak for G occurs at 788 mV, and its current is linearly related to the concentration of G in the range from 0.025 to 1.00 μM. The detection limits are 0.017 μM for A and 0.008 μM for G (at S/N = 3), respectively. The modified electrode displays good reproducibility and selectivity for the determination of A and G. The sensor was applied to quantify A and G in fish sperm DNA with satisfactory results.

We report on a novel nonenzymatic sensor platform for the determination of hydrogen peroxide and glucose. It is based on a carbon paste electrode that was modified with Co0.4Fe0.6LaO3 nanoparticles synthesized by the sol–gel method. The structure and morphology of Co0.4Fe0.6LaO3 nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical performance of this sensor was evaluated by cyclic voltammetry and amperometry, and the results demonstrated that it exhibits strong electrocatalytical activity towards the oxidation of H2O2 and glucose in an alkaline medium. The sensor has a limit of detection as low as 2.0 nM of H2O2 and a linear range that extends from 0.01 to 800 μM. The response to glucose is characterized by two analytical ranges of different slope, viz. from 0.05 to 5 μM and from 5 to 500 μM, with a 10 nM limit of detection. The glucose sensor has a fast response and good long term stability.

A novel non-enzymatic hydrogen peroxide (H2O2) sensor based on the MnO2-ordered mesoporous carbon (OMC) nanocomposite modified glassy carbon electrode (MnO2/OMC/GCE) was developed. OMC was synthesized and dropped onto the surface of glassy carbon electrode, and MnO2 nanoparticles were then electrodeposited on the surface of OMC to fabricate the MnO2/OMC/GCE. The electrochemical behaviors of H2O2 at the modified electrode were investigated by cyclic voltammetry and amperometry. The results showed that the MnO2/OMC/GCE exhibited excellent electrocatalytic activity toward H2O2. Optimization of measurement parameters such as the amount of MnO2, applied potential and pH value were studied in detail. Under the optimum conditions, the calibration curve for H2O2 determination was linear in the range from 5 × 10−7 to 6 × 10−4 M with a detection limit of 7.0 × 10−8 M (S/N = 3), and the sensitivity of the sensor was calculated to be 806.8 μA mM−1 cm−2.Graphical abstractAmperometric responses of different electrodes with successive addition of 10 μM H2O2 into PBS (0.1 M, pH 8.0) solution. Applied potential: 0.45 V.Highlights► A novel MnO2-ordered mesoporous carbon nanocomposite modified electrode was prepared. ► The modified electrode showed excellent electrocatalytic ability to H2O2 oxidation. ► The non-enzymatic sensor exhibited wide linear range and high sensitivity for H2O2.

In this work, a poly(alizarin red)/Graphene composite film modified glassy carbon electrode (PAR/Graphene/GCE) was prepared for simultaneous determination of four DNA bases (guanine, adenine, thymine and cytosine) without any pretreatment. The morphology and interface property of PAR/Graphene films were examined by scanning electron microscopy and electrochemical impedance spectroscopy. The PAR/Graphene/GCE exhibited excellent electrocatalytic activity toward purine (guanine and adenine) and pyrimidine (thymine and cytosine) in 0.1 M phosphate buffer solution (pH 7.4). Under optimum conditions, differential pulse voltammetry was used to detect the oxidation of purine and pyrimidine. The results showed that PAR/Graphene/GCE exhibited well-separated peaks, low detection limit, high sensitivity and wide linear range for simultaneous detection of purine and pyrimidine. The proposed sensor also has good stability and reproducibility. Furthermore, the modified electrode was applied for the detection of DNA bases in a fish sperm DNA sample with satisfactory results.Graphical abstractDPVs of PAR/Graphene/GCE (a) and the bare GCE (c) in 0.1 M PBS containing 50.0 μM G, 50.0 μM A, 100.0 μM T and 100.0 μM C, (b) PAR/Graphene/GCE in 0.1 M PBS.Highlights► The sensor exhibited well-separated peaks and low detection limit. ► The sensor possesses high sensitivity and wide linear range. ► The sensor was used for simultaneous detection of G, A, T and C successfully. ► The sensor was applied in a fish sperm DNA sample with satisfactory results. ► The proposed sensor has good stability and reproducibility.

A novel Co3O4 nanoparticles-decorated graphene (GR) composite was synthesized by electro-deposition and characterized by scanning electron micrographs, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Then, amperometric biosensors based on a Co3O4 nanoparticles-decorated GR composite modified glassy carbon electrode (GCE) were developed for the sensitive determination of L-tryptophan (Trp). The direct electrooxidation behaviors of Trp on the Co3O4/GR/Nafion/GCE were carefully investigated by cyclic voltammetry and square wave voltammetry. The results indicated that Trp showed an increase of the oxidation peak current with a negative shift of the oxidation peak potential compared with that on the bare GCE. Under optimum conditions, the proposed biosensor can be applied to the quantification analysis of Trp with a wide linear range covering 0.05–10 μM (R = 0.996) and a low detection limit of 0.01 μM. The experimental results also showed that the sensor exhibited good reproducibility, long-term stability as well as high selectivity. Moreover, the novel biosensor for the detection of Trp in a real amino acid sample with satisfactory results has been proved.

A novel, sensitive, and convenient method for the determination of uracil and thymine by functionalized CdS nanoparticles (NPs) was proposed. CdS NPs were prepared by hydrothermal process and modified with thioglycollic acid (TGA) in aqueous solution. The fluorescence intensity of functionalized CdS NPs was quenched in the presence of uracil or thymine. Under optimal conditions, the relative fluorescence intensity (F0/F) was proportional to the concentration in the range of 9.0×10−6–1.0×10−4 mol/L for uracil (r=0.9985) and 8.8×10−7–1.5×10−4 mol/L for thymine (r=0.9960). The corresponding detection limits were 9.6×10−7 mol/L and 3.2×10−7 mol/L, respectively. In addition, the possible quenching mechanism was also discussed.Highlights► Nano-CdS fluorescence probes were synthesized with good optical properties. ► Uracil and thymine were successfully detected by CdS fluorescence probes. ► Wide linear ranges and low detection limits were obtained.

A sensitive electrochemical sensor for amino acids was built based on perovskite LaNi0.5Ti0.5O3 (LNT) modified carbon paste electrode. The modified electrode was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The electrocatalysis of LNT to the oxidation of l-cysteine (l-cys) was studied by cyclic voltammetry in NaOH solution, and the experimental conditions were investigated in detail, such as NaOH concentration and the applied potential. Under the optimal conditions, the reported sensor was applied to the detection of l-cys, l-tryptophane (l-trp), l-alanine (l-ala) and l-phenylalanine (l-phe). In addition, the reported amino acids sensor exhibited good reproducibility, long-term stability, and fast current response.Highlights► An amino acid electrochemical sensor based on perovskite LaNi0.5Ti0.5O3 (LNT) modified carbon paste electrode. ► Electrocatalysis for l-cysteine oxidation. ► Experimental conditions were studied in detail. ► l-Cysteine, l-tryptophane, l-alanine and l-phenylalanine were detected under the optimum conditions.

In this study, a polymerized film of melamine (PMel) was first prepared on the surface of glassy carbon electrode (GCE) in acidic solution by cyclic voltammetry. Scanning electron microscopy, Fourier transforms infrared spectroscopy and electrochemical techniques were used for characterization of the modified electrode surface. The electrochemical activity of the poly-melamine film modified glassy carbon electrode (PMel/GCE) was primarily tested for electrochemical catalyzes of guanine (G), adenine (A) and epinephrine (EP) in 0.1 M phosphate buffer solution (pH 4.5). The oxidation currents of G, A, and EP at the PMel/GCE increased 9, 7 and 13 times respectively compared with that of bare GCE. In the detection of the three aforementioned analytes using square wave voltammetry, the linear ranges of the peak currents at the PMel/GCE were 0.1–50 μM G, 0.1–60 μM A and 0.1–100 μM EP with detection limits of 0.08 μM G, 0.07 μM A and 0.05 μM EP, respectively. Furthermore, the prepared electrode displayed voltammetric responses with high sensitivity, good selectivity and reproducibility for A, G, and EP in optimal conditions, making it very suitable for determination of the three components.Highlights► A novel poly-melamine film modified glassy carbon electrode. ► The sensor was prepared for sensitive detection of guanine, adenine and epinephrine. ► Obviously catalytic performance to the electrochemical response. ► It showed high stability, repeatability, reproducibility, good sensitivity.

A glassy carbon electrode modified with the composite film of MnO2 and Nafion was used for the sensitive voltammetric determination of epinephrine (EP) and the modified electrode exhibited excellent electrocatalytic activity to EP. MnO2 in various structural forms has shown superior electrochemical performance, high pseudocapacitance along with the cost-effective and environment friendly nature and thus attracting enormous attention. The electrochemical response characteristics of the modified electrode toward EP were investigated by cyclic voltammetry and differential pulse voltammetry. Under the optimum conditions, the cathodic peak current increases linearly with increasing EP concentration in the ranges of 0.03–10 μM and 10–100 μM, with the correlation coefficient of 0.999 and 0.993, respectively. The sensitivity of the modified electrode is calculated to be 5775 μA mM−1 cm−2 and the detection limit is 0.005 μM (based on the S/N = 3). The measurement repeatability of the MnO2/Nafion/GCE was examined with the same electrode and the relative standard deviation (RSD) was 0.86% for seven successive assays. Three modified electrodes showed an acceptable reproducibility with RSD of 1.13% for amperometric determination at 100 μM EP. The interferences of some metal ions and organic compounds have been investigated by cyclic voltammetry. The modified electrode can be used for the determination of EP in practical injection.Highlights► We have prepared a new MnO2/Nafion modified electrode. ► The modified electrode has been used for the detection of epinephrine (EP). ► The method exhibited high sensitivity and low detection limit.

A novel and sensitive method based on the quenching of the fluorescence intensity of functionalized ZnS nanoparticles (NPs) by nevirapine was proposed in this paper. ZnS NPs were synthesized by a hydrothermal method and modified with thioglycolic acid (TGA). The water-soluble modified ZnS NPs were characterized using transmission electron microscopy, X-ray diffractometry, zeta potential/particle sizing and photoluminescence spectroscopy. Under the optimum conditions, the relative fluorescence intensity (log(F0/F)) of ZnS NPs is linearly proportional to the nevirapine concentration ranging from 4.6 to 200 μM, and the limit of detection for nevirapine was found to be 0.73 μM. Moreover, the possible quenching mechanism was also investigated. The present method is convenient and suitable for practical applications.

A novel nonenzymatic hydrogen peroxide (H2O2) sensor based on LaNi0.5Ti0.5O3/CoFe2O4 nanoparticles modified glassy carbon electrode (LNT–CFO/GCE) was proposed. Perovskite-type nanocomposite oxide LaNi0.5Ti0.5O3/CoFe2O4 was synthesized by sol–gel method and characterized by X-ray diffraction and transmission electron microscopy. The electrochemical properties of the modified electrode were studied by cyclic voltammetry and amperometry, which showed an excellent electrocatalytic activity for the oxidation of H2O2. Under the optimum conditions, the linear response was obtained in the range of 0.1 μM to 8.2 mM, with the correlation coefficient of 0.997. The sensitivity of the modified electrode was calculated to be 3.21 μA μM−1 cm−2 and the detection limit was 23 nM (based on the S/N = 3).Graphical abstractHighlights► The sensor exhibited wider linear range of concentration change and high sensitivity compared with those previously reported. ► A novel electrocatalyst (LaNi0.5Ti0.5O3/CoFe2O4) which overcomes the disadvantages of native enzymes was obtained. ► At the same time, it is expected to overtake expensive Pt nanoparticles in H2O2 determination.

L-Cysteine capped CdTe nanoparticles (NPs) were synthesized in aqueous medium, and their application as fluorescence probes in the determination of paracetamol was studied. The L-cysteine capped CdTe NPs were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry, ultraviolet-visible and Fourier transform infrared spectrometry. Based on the distinct fluorescence quenching of CdTe fluorescence probes in the presence of paracetamol, a simple, rapid and specific method for paracetamol determination was presented. Under optimum conditions, the relative fluorescence intensity of CdTe NPs was linearly proportional to paracetamol concentration from 1.0 × 10−8 mol/L to 1.6 × 10−7 mol/L with a detection limit of 4.2 × 10−9 mol/L. The proposed method was applied to detect paracetamol in commercial tablets with satisfactory results.

Cupric acetate/polyacrylonitrile composite nanofibers were prepared by electrospinning and hollow copper oxide (CuO) particles were produced after subsequent thermal treatment process. The electrospun hollow CuO particles modified carbon paste electrode (CPE) was demonstrated for the first time for nonenzymatic hydrogen peroxide (H2O2) sensor. The structures and morphologies of hollow CuO particles were characterized by scanning electron microscopy and X-ray diffraction spectrum. The assay performance of the modified sensor to H2O2 was evaluated by cyclic voltammetry and amperometry, revealing high sensitivity (1746.50 μA mM−1 cm−2), low detection limit (0.022 μM) and wide linear response of determination of H2O2 oxidation in the range of 0.05 μM to 1.00 mM.Graphical abstractHighlights► We prepared cupric acetate/polyacrylonitrile composite nanofibers by electrospinning. ► Hollow CuO particles were obtained after the calcinations of nanofibers. ► The CuO modified electrode displayed excellent results in H2O2 determination. ► The H2O2 sensor had low detection limit and high sensitivity. ► The CuO modified can be applied to the determination of real samples.

A novel nitrite sensor was fabricated based on a graphene/polypyrrole/chitosan nanocomposite film modified glassy carbon electrode. The nanocomposite film was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The electron transfer behaviour of the modified electrodes was investigated in [Fe(CN)6]3−/4− redox probe using cyclic voltammetry and electrochemical impedance spectroscopy. Differential pulse voltammetry and amperometry were used to study the electrochemical properties of the proposed sensor. Under optimum conditions, the sensor exhibited good reproducibility and stability for nitrite determination. Linear response was obtained in the range of 0.5–722 μM with a detection limit of 0.1 μM (S/N = 3) for nitrite determination.

A horseradish peroxidase (HRP) biosensor based on alumina (Al2O3) nanoparticles-chitosan (CHIT) nanocomposites was developed for the detection of phenolic compounds. UV-Vis spectra and Fourier transform infrared spectra showed that HRP retained its original structure on the Al2O3/CHIT film. The surface morphologies of the composite films were characterized by scanning electron microscopy. Cyclic voltammetry and amperometry were used to study the proposed electrochemical biosensor. Optimization of the experimental parameters was performed with regard to pH, applied electrode potential and the concentration of hydrogen peroxide. The linear range, sensitivity and detection limit of the biosensor were investigated for eight phenolic compounds. In particular, the linearity of the biosensor for the detection of hydroquinone was obtained from 5 × 10−9 M to 7 × 10−5 M with a detection limit of 1 nM (based on the S/N = 3). The optimized biosensor for hydroquinone determination displayed a high sensitivity of 518.4 nA μM−1 with a response time of ∼5 s.

A biosensor for hydrogen peroxide was constructed by immobilizing horseradish peroxidase on chitosan-wrapped NiFe2O4 nanoparticles on a glassy carbon electrode (GCE). The electron mediator carboxyferrocene was also immobilized on the surface of the GCE. UV–vis spectra, Fourier transform IR spectra, scanning electron microscopy, and electrochemical impedance spectra were acquired to characterize the biosensor. The experimental conditions were studied and optimized. The biosensor responds linearly to H2O2 in the range from 1.0 × 10−5 to 2.0 × 10−3 M and with a detection limit of 2.0 × 10−6 M (at S/N = 3).

An amperometric biosensor based on horseradish peroxidase (HRP) and γ-Al2O3/chitosan composite film at a glassy carbon electrode has been developed. Hydrogen peroxide (H2O2) was detected with the aid of ferrocene monocarboxylic acid mediator to transfer electrons between the electrode and HRP. The morphology and composition of the modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and amperometry. The effects of HRP concentration, the applied potential, and the pH values of the buffer solution on the response of the sensor were investigated for optimum analytical performance. The proposed biosensor showed high sensitivity (0.249 A M−1 cm−2) and a fast response (<5 s) to H2O2 with the detection limit of 0.07 μM. The linear response range of the enzyme electrode to H2O2 concentration was from 0.5 to 700 μM with a correlation coefficient of 0.9998. The apparent Michaelis-Menten constant of the biosensor was calculated to be 0.818 mM, exhibiting a high enzymatic activity and affinity for H2O2.

A novel nanostructured perovskite-type composite oxide LaNi0.5Ti0.5O3–NiFe2O4 (LNT–NFO) was synthesized by sol–gel method and characterized by X-ray diffractometer (XRD) and transmission electron microscopy (TEM). Amperometric glucose biosensors based on the carbon paste electrode (CPE) were constructed by immobilizing glucose oxidase (GOD) with LNT–NFO and the experimental conditions such as the amount of GOD, pH value, and applied potential were investigated. Under the optimum conditions, the electrochemical performances of the LNT–NFO with different ratios of LNT-NFO (10:1, 20:1, 30:1) modified CPE have been researched on the oxidation of glucose. The results show that LNT–NFO (20:1) can immobilize GOD more effectively. The biosensor based on LNT–NFO/CS/GOD modified CPE exhibits good reproducibility, stability and selectivity in glucose determination with linear signal-to-glucose concentration range of 0.5–10 mM and a detection limit (S/N = 3) of 0.04 mM.

A novel sensitive nonenzymatic glucose sensor was reported based on perovskite LaNi0.5Ti0.5O3 (LNT) modified carbon paste electrode (CPE). The surface characterization of the modified electrode and the bare CPE was examined by scanning electron microscopy (SEM). The high electrochemical activity of LNT to electrocatalytic oxidation of glucose in alkaline medium was characterized by cyclic voltammetry and amperometry, and the experimental conditions such as the amount of LNT, the concentration of NaOH and the applied potential were investigated in detail. The glucose sensor was applied to the quantification of glucose with a high sensitivity of 1630.57 μA mM−1 cm−2 and a low limit of detection of 0.07 μM. The novel glucose sensor also exhibited good reproducibility, long-term stability, as well as high selectivity with no interference from common interfering substances such as ascorbic acid, dopamine and uric acid.

In this paper, ZnSe nanoparticles, which were modified with mercaptoacetic acid (MAA), worked as novel fluorescence sensors for the quantitative determination of copper(II) and nickel(II). Under the optimal conditions, the fluorescence intensities of functionalized ZnSe nanoparticles were quenched by the addtion of copper(II) or nickel(II) ions, there were linear relationships between the relative fluorescence intensity (logF0/F) and the concentration in the range of 140–2,000 μg/L for copper(II) (R = 0.9973) and 30–1,000 μg/L for nickel(II) (R = 0.9992), the limits of detection were 50 μg/L and 5 μg/L, respectively.

A reliable and simple sensor was fabricated by modifying a carbon paste electrode with nanosized gold particles and poly (glutamic acid) for determination of paracetamol (PAR). The modified electrode exhibited an effective catalytic response to the oxidation and reduction of PAR with good reproducibility and stability. The determination was carried out by differential pulse adsorptive stripping voltammetry after a 30 s accumulation time with an open circuit potential and under stirring. The calibration curve is linear in the range from 0.05 to 70 μM of PAR (with a correlation coefficient of 0.9990), and the sensitivity is 1.51 μA·μM-1. The modified electrode was used to detect PAR in commercial tablets.

A glassy carbon electrode (GCE) modified with the film composed of chitosan incorporating cetylpyridine bromide is constructed and used to determine uric acid (UA) and ascorbic acid (AA) by differential pulse voltammetry (DPV). This modified electrode shows efficient electrocatalytic activity and fairly selective separation for oxidation of AA and UA in mixture solution. UA is catalyzed by this modified electrode in phosphate buffer solution (pH 4.0) with a decrease of 80 mV, while AA is catalyzed with a decrease of 200 mV in overpotential compared to GCE, and the peak separation of oxidation between AA and UA is 260 mV, which is large enough to allow the determination of one in presence of the other. Under the optimum conditions, the anodic peak currents (Ipa) of DPV are proportional to the concentration of UA in the range of 2.0 × 10−6 to 6.0 × 10−4 M, with the detection limit of 5.0 × 10−7 M at a signal-to-noise ratio of 3 (S/N = 3) and to that of AA in the range of 4.0 × 10−6 to 1.0 × 10−3 M, with the detection limit of 8.0 × 10−7 M (S/N = 3).

ZnS nanoparticles were prepared by hydrothermal method and modified with mercaptoacetic acid in this paper. The functionalized nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffractometer (XRD) and photoluminescence spectroscopy. They were used as fluorescence probes in the determination of uracil and thymine. Under the optimum conditions, the fluorescence of functionalized ZnS nanoparticles was quenched by uracil and thymine, respectively. The responses are linearly proportional to the concentrations of uracil and thymine both between 0.8 × 10−5 and 9.6 × 10−5 mol L−1and the limits of detection are 0.9 × 10−6 and 0.4 × 10−5 mol L−1 for uracil and thymine, respectively.

The oxidative electrochemistry of nitrite was investigated using a glassy carbon electrode modified with surfactants such as didodecyldimethylammonium bromide (DDAB), Tween-80, and sodium dodecylbenzenesulfonate, respectively. Nitrite oxidation proceeds best in the presence of DDAB. The electrode exhibited good sensitivity and fast response, with a linear dynamic range between 1.0 and 80 μM of nitrite, and a sensitivity of 0.04 µA·µM−1. The electrode was successfully applied to the determination of nitrite in spiked real water samples.

Luminescent quantum dots (QDs)-semiconductor nanocrystals were promising alternative to organic dyes for fluorescence-based applications. In this paper, we developed procedures to use mercaptoacetic acid (MAA) to modify ZnSe nanoparticles and made the nanoparticles to be soluble for the quantitative and selective determination of bovine serum albumin (BSA). Maximum fluorescence intensity was produced at pH 7.0, with excitation and emission wavelengths at 242 and 348 nm, respectively. Under optimal conditions, the straight line equation: △F = 0.38 + 0.34 C (μg/ml) was found between the relative fluorescence intensity and the concentration of BSA in the range of 9.6–124.8 μg/ml, and the limit of detection was 2 μg/ml.

Cyclic voltammetry was used to investigate the electrochemical reduction of nitrophenol isomers at a glassy carbon electrode modified with carbon nanotubes, and a derivative voltammetric technique was adopted to improve the resolution and enhance the determination sensitivity. In 0.1 mol L−1 HAc–NaAc buffer solution (pH 5.0), the modified electrode showed a good electrocatalytic response towards nitrophenol isomers. Through a derivative technique, the peak currents increased significantly and the reduction peaks of nitrophenol isomers could be separated, so the method could be applied to direct simultaneous determination without preseparation. The linear calibration ranges were 4.0 × 10−6 to 2.0 × 10−3 mol L−1 for o-nitrophenol, 1.0 × 10−5 to 1.0 × 10−3 mol L−1 for m-nitrophenol and 2 × 10−6 to 4.0 × 10−3 mol L−1 for p-nitrophenol, with detection limits of 5.0 × 10−7, 6.0 × 10−6 and 4.0 × 10−7 mol L−1, respectively.

The tetragonal YVO4 nanocrystals are facilely prepared via a hydrothermal solid-phase synthesis method directly utilizing bulk phase materials of V2O5 and Y2O3 as precursor. Whether additives (acid and EDTA) exist or not, the reaction can be performed in the mild temperature range from 130 to 200 °C. The products are characterized with XRD, FTIR, TEM and PL. The effect of acid and amounts of EDTA on the morphology of the product is investigated. The YVO4 nanoparticles exhibit novel photoluminescence emission bands at 330 and 606 nm under 254 nm excitation. A growth mechanism of yttrium orthovanadate is proposed.

Being an accurate and stable algorithm, Doolittle Decomposition Algorithm (DDA) was first introduced into the chemistry field. The basic principle of Doolittle Multivariate Calibration Algorithm (DMCA) was investigated, and the chromogenic system of W, Mo, Ti–SAF with overlapping absorption peaks was analyzed by DMCA. The computational relative standard deviation with DMCA is within ± 8.0% which was better than the result of K-Matrix (within ± 10.0%), the comparison indicated the superiority of Doolittle Decomposition Algorithm in the concentration analyzing. It was demonstrated that DDA can avoid matrix inverting, reduce the orders of matrixes and speed up the operation of matrixes. So it has bright prospects in chemometrics.

This paper has adopted a fast and convenient analytical technique to detect dinitrophenol isomers directly and simultaneously. In 0.1 mol L−1 HAc–NaAc buffer solution (pH 5.8), 2,4- and 2,5-dinitrophenol exhibited good resolution by DPV at the GC electrode. By using the surfactant of cetyl trimethyl ammonium bromide, the reduction peaks currents were enhanced and the detection sensitivity was improved dramatically. The action mechanism was investigated in detail and some valuable message has been found. The linear calibration ranges from 1.0 × 10−6 to 8.0 × 10−4 mol L−1 for both 2,4- and 2,5-dinitrophenol, with detection limits of 2.4 × 10−7 for 2,4- and 1.5 × 10−7 mol L−1 for 2,5-dinitrophenol. This method was applied in the determination of dinitrophenol isomers in model water sample, and the recovery was from 98% to 103%.

•A bioinspired MIECS was developed for ultra-trace CHO detection based on MIP-AuNPs-PDA-DGr/GCE.•The bioinspired PDA coated AuNPs grew to micro-sized Au flowers.•The MIECS possessed a specific affinity for CHO and the linear range was between 10−18 and 10−13 M.•The PDA films were used to achieve better imprinted effect and waste less time in preparation than self-assembly monolayers.A novel imprinted sensor for ultra-trace cholesterol (CHO) detection based on electropolymerized aminothiophenol (ATP) molecularly imprinted polymer (MIP) on a glassy carbon electrode (GCE) modified with dopamine@graphene (DGr) and bioinspired Au microflowers has been developed in this work. As the specific recognition element, the bioinspired Au microflowers were formed by Au nanoparticles (AuNPs) and wrapped by bionic polydopamine film (PDA) through electropolymerization method. These excellent biocompatible materials could capture the target CHO effectively. The morphology of the MIP modified electrode was characterized by scanning electron microscopy (SEM) and atomic force microscope (AFM). The hydrogen-bonding interaction between templates and monomers was characterized by ultraviolet spectroscopy. Under the optimal experimental conditions, the sensor's linear response range was between 10−18 and 10−13 M, with a detection limit of 3.3×10−19 M, which was much more sensitive than most available CHO detection methods in previously reports. Moreover, the MIP sensor exhibited high sensitivity for CHO, low interference, and good stability. The human serum samples analysis confirmed the applicability of this MIP sensor to quantitative analysis of ultra-trace CHO.

Graphite nanoparticles originated from high purity graphite crucible were used for deoxidization and purification of Li2BeF4 molten salt containing a bit of (NH4)2BeF4 under high temperature vacuum condition. And the mechanism of deoxidization and purification via graphite nanoparticles was put forward based on analysis of sample characterization and chemical reaction Gibbs free energy calculation. The morphology, particle size, chemical composition and crystal structure of graphite nanoparticles in Li2BeF4 molten salt were characterized by High Resolution Transmission Electron Microscopy (HRTEM, SAED and EDS). Phase analysis, total oxygen content, full elemental and anion concentration for as-prepared Li2BeF4 products were studied by X-Ray Diffraction (XRD), LECO nitrogen-oxygen analyzer, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Ion Chromatography (IC), respectively. The results of sample characterization showed that graphite nanoparticles in Li2BeF4 molten salt were the poly-crystal round sheet shape with an average diameter of <100 nm. The concentration of total oxygen, sulfur and nickel in as-prepared Li2BeF4 molten salt after treatment were 548 ppm, <0.6 ppm and <0.4 ppm, respectively. Experiment and calculation all showed that SO42− and NO3− could react with carbon at 700 °C. And vacuum degassing play an excellent role in deoxidization and purification for Li2BeF4 molten salt via graphite nanoparticles.

In this paper, LaNi0.6Co0.4O3 (LNC) nanoparticles were synthesized by the sol–gel method, and the structure and morphology of LNC nanoparticles were characterized by X-ray diffraction spectrum, scanning electron microscopy and transmitting electron microscopy. And then, LNC was used to modify carbon paste electrode (CPE) without any adhesive to fabricate hydrogen peroxide and glucose sensor, and the results demonstrated that LNC exhibited strong electrocatalytical activity by cyclic voltammetry and amperometry. In H2O2 determination, linear response was obtained in the concentration range of 10 nM–100 μM with a detection limit of 1.0 nM. In glucose determination, there was the linear region of 0.05–200 μM with a detection limit of 8.0 nM. Compared with other reports, the proposed sensor also displayed high sensitivity toward H2O2 (1812.84 μA mM−1 cm−2) and glucose (643.0 μA mM−1 cm−2). Moreover, this prepared sensor was applied to detect glucose in blood serum and hydrogen peroxide in toothpaste samples with satisfied results, indicating its possibility in practical application.Graphical abstractCVs recorded on the bare CPE (a) and LNC/CPE (c) with 0.3 mM H2O2, LNC/CPE (b) without H2O2 in 0.1 M NaOH. Scan rate: 100 mV s−1.Download full-size imageHighlights► The sensor exhibited wide linear range and low detection limit. ► The sensor possesses high sensitivity and fast response. ► The sensor was used for detection of hydrogen peroxide and glucose. ► The proposed sensor has good stability and reproducibility. ► The sensor was applied in toothpaste and serum samples with satisfactory results.

A novel and highly sensitive fluorescence probe has been developed for determination of ascorbic acid (AA) based on the distinct fluorescence quenching of Mn-doped CdTe fluorescence emission in the presence of AA. Mn-doped CdTe quantum dots were prepared by using inorganic salts as precursors and L-cysteine as the stabilizer in an aqueous system. Their optical properties were characterized by ultraviolet-visible spectrometry, spectrofluorometry, structural features by X-ray diffraction spectrometry, transmission electron microscopy, Fourier transform infrared spectrometry, and exact composition by energy dispersive spectrometry, respectively. Under the optimum conditions, the response is linearly proportional to the concentration of AA in the range of 0.4 to 10 nM with an extremely low detection limit of about 0.081 nM. The newly developed method was successfully applied for the determination of AA in pharmaceutical tablets with good recoveries.

We report a sensor platform for the determination of L-tryptophane. It is based on a carbon paste electrode that was modified with LaCoO3 poriferous nanofibers that were synthesized by electrospinning and subsequent thermal treatment. The structures and morphologies of LaCoO3 poriferous nanofibers were characterized by X-ray diffraction spectrum and scanning electron microscopy. The electrochemical performance of the sensor was evaluated by cyclic voltammetry and amperometry, and the results demonstrated that it exhibits strong electrocatalytical activity towards the oxidation of L-tryptophan in 0.1 mol L−1 phosphate buffer solution (pH 3.0). The linear range of L-tyrosine was 5.0 × 10−8 to 5.0 × 10−6 mol L−1 with a low detection limit down to 1.0 × 10−8 mol L−1. Moreover, the modified electrode exhibited high selectivity, long-term stability and fast current response, demonstrating its feasibility for the analytical purpose.

A novel poly-sulfosalicylic acid-modified glassy carbon electrode (PSA/GCE) was developed for the detection of roxithromycin (RM) and its simultaneous determination with dopamine (DA). The morphologies and interface properties of the PSA film were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Fourier transform infrared (FTIR) spectra indicated that PSA was successfully modified on the electrode. The electro-catalytic oxidation of RM on the PSA/GCE was investigated, individually and simultaneously, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions. The proposed method exhibited a wide linear dynamic range from 2 × 10−8 to 1 × 10−5 M with a low detection limit (S/N = 3) of 6.67 × 10−9 M for roxithromycin. The modified electrode showed good stability, reproducibility and high selectivity, and demonstrated its feasibility for analytical purposes and human serum samples.

In this paper, a novel method was developed for rapid and quantitative determination of cephalexin on the basis of the fluorescence quenching of L-cysteine capped core–shell CdTe/ZnS nanoparticles (NPs). The functionalized CdTe/ZnS NPs were successfully synthesized in aqueous solution. L-Cysteine capped CdTe/ZnS NPs were characterized by the means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Experimental results displayed that the fluorescence intensity of CdTe/ZnS NPs reduced in the presence of cephalexin due to interaction between L-cysteine capped CdTe/ZnS NPs and cephalexin, with the emission wavelength at about 665 nm. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of cephalexin ranging from 3.4 × 10−6 to 1.0 × 10−4 M with a detection limit of 0.83 × 10−6 M. The L-cysteine capped CdTe/ZnS NPs fluorescence probe showed an obvious and good response to cephalexin, and the result was also satisfactory when it was applied to analyzing cephalexin in a real sample.

The electrochemical detection of hydrogen peroxide in alkaline solution was performed on a La0.7Sr0.3Mn0.75Co0.25O3 (LSMCO) nanofiber modified carbon paste electrode. Perovskite-type oxide LSMCO nanofibers were prepared by electrospinning and calcination. The morphologies, structures, and electrochemical behaviours of the nanofibers were characterized by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and cyclic voltammetry. The modified electrode shows excellent electrocatalytic activity towards hydrogen peroxide. Under optimal conditions, the linear response was obtained in the range of 0.5–1000 μM, with high sensitivity and a low limit of detection.

A poly-Ni(II)–curcumin (curcumin: 1,7-bis[4-hydroxy-3-methoxyphenyl]-1,6-heptadiene-3,5-dione) composite film modified electrode was prepared for amperometric determination of β-nicotinamide adenine dinucleotide (NADH). Scanning electron microscopy and Energy Dispersive X-ray spectroscopy were used to examine the morphology and interface property of the Ni(II)–curcumin film. Under optimum conditions, the amperometric detection of NADH provided a wide linear detection range (0.3–300 μM), high sensitivity (230.02 μA mM−1 cm−2) and low limit of detection (LOD = 0.18 μM, S/N = 3). Moreover, the modified electrode showed good stability and reproducibility, indicating that it can improve the analysis signal of NADH in a very convenient way.

A novel and sensitive method based on the quenching of the fluorescence intensity of functionalized ZnS nanoparticles (NPs) by nevirapine was proposed in this paper. ZnS NPs were synthesized by a hydrothermal method and modified with thioglycolic acid (TGA). The water-soluble modified ZnS NPs were characterized using transmission electron microscopy, X-ray diffractometry, zeta potential/particle sizing and photoluminescence spectroscopy. Under the optimum conditions, the relative fluorescence intensity (log(F0/F)) of ZnS NPs is linearly proportional to the nevirapine concentration ranging from 4.6 to 200 μM, and the limit of detection for nevirapine was found to be 0.73 μM. Moreover, the possible quenching mechanism was also investigated. The present method is convenient and suitable for practical applications.